The proposal postulates that in pediatric patients suffering from type I or insulin-dependent diabetes mellitus (IDDM) abnormal vascular reactivity (VR) is a physiologic marker for a pre-hypertensive state, reflecting changes to vessel walls. We hypothesize that it is an early indicator of the microangiopathic process underlying diabetic vascular complicaitions (DVC) and could point to patients at increased risk for developing DVC such as retinopathy or nephropathy. We further postulate that abnormal VR can be reversed. As a measured non-invasively by physiological vascular responses and by markers in the urine or serum; reversal of abnormal VR could be achieved through tight diabetic control of blood glucose levels and possibly by the administration of an ACE-inhibitor medication (ie. Enalapril)